Arthroscopic procedures are becoming an increasingly popular approach for less-invasive orthopedic diagnosis and therapy. As clinical experience is gained, more advanced procedures have become feasible, demanding more sophisticated and higher performance instrumentation and methods. A significant limitation on arthroscopic procedures is the lack of accessibility to specific joint spaces, for example, in the knee.
Curved guiding cannulas have been developed to assist in delivery of flexible probes such as needles to tissue otherwise unreachable to the arthroscopist without significant tissue trauma. Such cannulas are typically rigid, hollow, tubular devices usually constructed of stainless steel or plastic. These devices can be provided with special features such as finger grips or ports at the proximal end to facilitate manual control and/or fluid introduction and removal. The shafts are generally rigid to prevent collapse during use and to facilitate introduction of the cannula into the tissue. Rigidity also generally is required to adequately constrain and guide accessories passed through the cannula. The distal end usually is tapered radially inwardly to ease the insertion process.
Although probes may be used without such access cannulas, there are several distinct advantages to cannula use. First, once positioned, a cannula provides repeated access to the operative location without repeated puncturing of tissue. Second, some probes are not sufficiently rigid or controllable to assure proper navigation about anatomical variances without the use of a cannula. Finally, some probes have trauma producing features (e.g., cutting edges, rasps) which prohibit their insertion into tissue without the protection of a cannula.
Precisely curved cannulas theoretically may be capable of permitting access to remote areas of a joint such as a knee, but probes must be capable of navigating such curved passageways without being damaged themselves. For example, stainless steel needles used to suture tears in the meniscus of a knee are capable of navigating only relatively gentle curves without emerging from the distal end of a cannula with a permanent bend or set.